Amyotrophic Lateral Sclerosis (ALS) is a progressive neurodegenerative disease affecting over 5500 Americans each year. Onset of ALS usually occurs between ages 55 and 65, and the disease is invariably fatal. ALS occurs in both familial and sporadic variants; the only known cause of ALS is mutation to the SOD1 gene, which is present in twenty percent of familial cases. This mutation causes the SOD1 protein to misfold and aggregate, creating toxic plaques that are believed to cause motor neuron cell death. The long-term goal of this work is to identify the mechanisms of SOD1 aggregation, and prevent aggregation by the binding of designed small molecule drugs. A key step in the aggregation of SOD1, a homodimeric metallo-enzyme, is the dissociation of the dimer. Prevention of dissociation of SOD1 could prevent the formation of aggregates, and therefore prevent motor neuron death. In addition to mutation, post-translational modifications to SOD1 also cause increased dissociation of the dimer. Post-translational modification occurs in both mutant and wild-type SOD1, and could provide a link between familial and sporadic forms of ALS. Unlike mutation, modifications cause significant change in the structure of SOD1. Because post-translational modifications are present at high frequency in humans, with approximately fifty percent of SOD1 being modified, any drugs designed for SOD1 will need to take into account these structural changes. The aims of this research project are: (1) to determine the mechanism of dimer destabilization in post-translationally modified SOD1, and (2) to identify small molecules capable of binding to both post-translationally modified and unmodified SOD1 to stabilize the dimer interface. We hypothesize that modifications destabilize the dimer by disrupting interactions across the dimer interface. Further, we hypothesize that a small molecule bridging the two monomers can stabilize the dimer and rescue from the effects of mutation and modification. To achieve specific aim 1, we will perform Discrete Molecular Dynamics (DMD) simulations of modified and unmodified species of SOD1 in order to gain insight into the thermodynamic and structural effects of modifications. To achieve specific aim 2, we will identify candidate drug-binding pockets near the dimer interface of SOD1 and use a novel hybrid virtual screening technique incorporating DMD simulations to evaluate the binding of drug molecules to the identified pockets. If our proposed aims are achieved, we will (1) contribute a possible etiology and molecular mechanism for SOD1 toxicity in ALS linking familial and sporadic cases, and (2) identify new lead compounds toward the treatment of ALS and introduce a novel virtual screening method for the computational assay of small ligand binding incorporating ligand-protein dynamics as well as energetic contributions. Using the results of this proposal, we may build a clearer description of the determinants of SOD1 stability. This work will provide a description of a possible molecular etiology common to familial and sporadic ALS, as well as present a new strategy for the discovery of therapeutics.